WDM add/drop multiplexer module

ABSTRACT

A casing member for a WDM add/drop multiplexer unit, the casing member comprising a backplane for interconnection of components of the WDM add/drop multiplexer unit inserted in the casing member, and at least one heat sink opening formed in a wall of the casing member disposed to, in use, receive a heat sink structure of a component of the WDM add/drop multiplexer unit in a manner such that the heat sink structure is exposed to an ambient around the casing member when the component is mounted in the casing member, for facilitating maintaining a controlled temperature environment inside of the component.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application of the co-pendingU.S. patent application Ser. No. 10/028,745, filed on Dec. 21, 2001, andclaims priority of Australian patent application No. PS2771, filed onJun. 3, 2002.

FIELD OF THE INVENTION

The present invention relates broadly to a casing member for a WDMadd/drop multiplexer unit. The present invention also relates to anoptical network node and to an optical network.

BACKGROUND OF THE INVENTION

Optical networks may be classified into long haul optical networks,metro optical networks, access optical networks and enterprisegear-optical networks. Distinctions between the different types may in afirst instance be drawn on the basis of physical transmission distancescovered, decreasing from long haul optical networks down to enterprisegear-optical networks, with the latter being typically implementedwithin one location e.g. in one office building.

The different types of optical networks can also be distinguished interms of the physical environment in which in particular add/dropequipment is located. For example, for enterprise gear-optical networks,the add/drop equipment is typically located inside of air conditionedbuildings, and therefore no particular extreme temperature conditioncompliance is required to implement such optical networks. For long hauland metro optical networks, which typically involve very complex andexpensive equipment, add/drop equipment is typically located intelecommunications carriers central offices and points of presence andare subjected to a limited range of temperatures, which is sometimesreferred to as requiring the add/drop equipment to be carrier classcompliant. This temperature range is typically in the range of −5 to 55°C. as required for Telcordia NEBS level 3.

However, in access optical networks the add/drop equipment is typicallylocated in an outside plant (OSP) situation, and thus potentiallysubjected to a wider temperature range than e.g. carrier classcompliance requirements.

Currently, the only optical networks that can be implemented inscenarios where the required add/drop equipment is located in an OSPsituation are Time Domain Multiplexing (TDM) based networks. So far, WDMbased optical networks have not been deemed suitable for implementationin OSP situations, as currently available WDM equipment is not OSPcompatible. However, it would be desirable to implement WDM basedoptical networks in such an environment, to utilise the larger capacityin the optical domain in access optical networks. It would further bedesirable if such an implementation could be achieved in a compactdesign for the hardware involved.

At least preferred embodiments of the present invention seek to providea casing member for a WDM add/drop multiplexer module, suitable for usein an OSP situation and facilitating a compact hardware design.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention there isprovided a casing member for a WDM add/drop multiplexer unit, the casingmember comprising:

a backplane for interconnection of components of the WDM add/dropmultiplexer unit inserted in the casing member, and

at least one heat sink opening formed in a wall of the casing memberdisposed to, in use, receive a heat sink structure of a component of theWDM add/drop multiplexer unit in a manner such that the heat sinkstructure is exposed to an ambient around the casing member when thecomponent is mounted in the casing member, for facilitating maintaininga controlled temperature environment inside of the component.

In one embodiment, the heat sink opening is formed in the backwallincorporating the backplane.

A pair of heat sink openings may be formed in a mirrored configurationon either side of the backplane with respect to a centreplane halfwayalong the width of the casing member.

The casing member may further comprise a first key member arranged, inuse, to prevent a component of the WDM add/drop multiplexer unit fromcontacting the backplane, when said component is inserted with anincorrect orientation, and wherein the first key member is adapted tocooperate with a heat sink structure of said component.

In one embodiment, the casing member further comprises a second keymember arranged, in use, to prevent a component of the WDM add/dropmultiplexer unit from contacting the backplane, when said component isinserted with a correct orientation in another component's intendedslot, and wherein the second key member is adapted to co-operate with athird key member formed on said component.

Preferably, the casing member further comprises at least one ventopening in one wall of the casing member.

Advantageously, the casing member comprises at least one pair of ventopenings, the openings of the pair being formed in opposite walls of thecasing member.

In one embodiment, the at least one pair of vent openings is formed inthe sidewalls of the housing.

At least one pair of vent openings may be formed in the top and bottomwalls of the housing element.

In one embodiment, the housing element is adapted for mounting onto arack structure.

The housing element may be adapted to be mounted horizontally orvertically.

In one embodiment, the casing member further comprises a heat sink unitmounted onto the casing member and adapted, in use, when components ofthe WDM add/drop multiplexer unit are inserted in the casing member, tomake thermal contact with at least one of the components, forfacilitating maintaining a controlled temperature environment inside ofsaid component.

Preferably, the casing member comprises a locking member arranged, inuse, to cooperate with a corresponding locking member of one of thecomponents when the component is inserted to maintain the thermalcontact.

Advantageously, the locking member is arranged, in use, to co-operatewith the corresponding locking member to bias the component wheninserted.

The heat sink unit may be arranged in a manner such that, in use, theinterconnection to said component is releasable.

The heat sink unit may be incorporated in the backwall incorporating thebackplane.

In one embodiment, the heat sink unit is formed on the backplane.

The heat sink unit may comprise a plurality of substantially planar finsdisposed substantially parallel to the backwall of the casing member,and mounted by way of at least one longitudinal mounting memberexpanding substantially perpendicularly from the backwall. Accordingly,convection airflow between the fins is preferably not inhibited ineither a horizontal or a vertical mounting position of the casingmember.

The casing element may further comprise at least one fan device mountedon the outside of the housing element and disposed in a manner suchthat, in use when the heat sink structure of the component of the WDMadd/drop multiplexer unit extends through the heat sink opening of thehousing element, the heat sink structure is subjected to an airflowgenerated by the fan device.

In one embodiment, the casing member further comprises at least onebaffle structure externally mounted or formed on the casing member, andarranged in a manner such that in use when the casing member is mountedvertically into the rack structure, convection airflow from one heatsink structure or heat sink unit is diverted away from other heat sinkstructures or heat sink units.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described, byway of example only, with reference to the accompanying drawings.

FIG. 1 shows a perspective view of a casing embodying the presentinvention.

FIG. 2 shows a perspective view of the casing of FIG. 1, with the topcover removed and components of a WDM add/drop multiplexer unitinserted.

FIG. 3 is a perspective view of the casing of FIG. 1 with components ofa WDM add/drop multiplexer unit inserted.

FIG. 4 is a perspective view of another casing embodying the presentinvention.

FIG. 5 is a perspective view of another casing embodying the presentinvention.

FIG. 6 is a perspective view of another casing embodying the presentinvention.

FIG. 7 is a perspective view of a component of a WDM add/dropmultiplexer unit, embodying the present invention.

FIG. 8 is a perspective front view of the component shown in FIG. 7.

FIG. 9 is a schematic back view of another casing embodying the presentinvention.

FIG. 10 is a perspective view of a chassis member embodying the presentinvention.

FIG. 11 shows a perspective view of parts of a WDM multiplexer moduleembodying the present invention.

FIG. 12 shows a perspective view of an assembled WDM multiplexer moduleembodying the present invention.

FIG. 13 shows a perspective view of another chassis member embodying thepresent invention.

FIG. 14 is a schematic diagram illustrating a WDM add/drop multiplexerunit embodying the present invention.

FIG. 15 is a schematic diagram of a detail of FIG. 14.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In FIG. 1, a casing 10 embodying the present invention comprises top andbottom covers 12, 14 respectively. The casing 10 further comprises sidewalls 16, 18 respectively. Vent openings in the form of openings e.g. 20in a mesh-type structure 22 forming the side walls e.g. 16 areincorporated for, in use, fluid communication between the inside 24 ofthe casing 10 and the surrounding ambient. The casing 10 furthercomprises intermediate walls 26, 28.

As can be seen more clearly in FIG. 2, which shows the casing 10 withoutthe top cover 12 (see FIG. 1) and with components e.g. 30 of a WDMadd/drop unit inserted, the casing 10 further comprises a backplane inthe form of a mother board 32, for connection and interconnection of theinserted components e.g. 30, 34, and 36. The functionality of thevarious components will be described later with reference to FIGS. 14and 15. It is noted that in the embodiment shown in FIG. 2, the casing10 is designed in a manner such that the heat sink openings 38 and 42,and the backplane 32 are mirrored with respect to a centreplane halfwayalong the width of the casing 10. This enables an optimal spacingbetween the set of fins 44, 46, and 48. At the same time, to facilitatethat components 30 and 34, which, in end use, have differentfunctionality and specifications, may initially undergo the samemanufacturing steps and can be manufactured along the same productionline up to a certain step, the components 30 and 34 are inserted with a“swapped” orientation. In other words, in terms of the individualchassis/housing of the components, 30 and 34, they are disposed upsidedown with respect to each other. To prevent inadvertent insertion of thewrong component, the electrical connections to the backplane 32 arekeyed appropriately. Overall, the components 30, 34 are thushot-swappable on-site.

In the example embodiment, and as shown in FIG. 1, the casing member 10comprises two key members in the form of two banded flaps e.g. 15 formedon the top and bottom covers 12, 14 respectively, and in a mirroredfashion in relation to the centreplane halfway along the width of thecasing 10. In use, e.g. flap 15 will prevent component 30 (see FIG. 2)from being fully inserted in any slot in the incorrect orientation. Itwill be appreciated by the person skilled in the art that the flap 15 isdesigned in the example embodiment to abud the set of fins 44 (see FIG.2) or 48 (see FIG. 2), for preventing contact with the backplane 32 (seeFIG. 2) in those circumstances.

Furthermore, and referring now to FIG. 2, the casing 10 furthercomprises secondary key members in the form of protrusions formed onsidewalls 26, 28 respectively and extending towards the components 30and 34 respectively. The protrusions, which are hidden in FIG. 2 as willbe appreciated by the person skilled in the art, but are shown in FIG. 6at e.g. numeral 493, are arranged in a manner such that they cooperatewith protrusions, in the example embodiment in the form of screws shownin FIG. 12 at e.g. numeral 139) screwed onto the respective components30, 34 to prevent insertion of components 30, 34, would, into theposition intended for the other component to an extent that they makecontact with the backplane 32. It will be appreciated by the personskilled in the art, that accordingly, in the example embodiment, thecasing 10 is double-keyed to prevent wrong insertion of components 30,34.

It is noted that in the example embodiment, the respective contacts (notshown) on the backplane 32 intended for the components 30, 34 aredisposed in a manner such that their relative positioning on thebackplane 32 is effectively an upside down and left/right swappedconfiguration, which further facilitates that components 30 and 34 maybe manufactured along the same production line up to a certain step, asmentioned above. At the same time, wrong insertion of the individualcomponents in the swapped orientation in the other component's spot isprevented, in the example embodiment, through the secondary key memberas described above.

The casing 10 further comprises three heat sink openings 38, 40 and 42.The heat sink openings 38, 40, and 42 are each disposed in a manner suchthat heat sink structures in the form of sets of fins 44, 46, and 48respectively extend therethrough to be exposed to the ambient outside ofthe casing 10. The sets of fins 44, 46, and 48 are part of the insertedcomponents 30, e.g. 36, and 34 respectively, i.e. they are not mountedto or formed integrally with the casing 10. It will be appreciated by aperson skilled in the art that accordingly, unlike in prior art designs,in the casing 10 embodying the present invention the provision of heatsinks in the form of e.g. fins has been separated from the casing 10 perse. Rather openings 38, 40 and 42 are provided through which heat sinkstructures of individual components inserted in the casing 10 can bereceived and exposed to the ambient outside the casing 10. It will beappreciated that this increases the flexibility concerning temperaturecontrol requirements of e.g. a WDM add/drop multiplexer unit mounted byway of the casing 10, as compared to prior art designs in which suchheat sink structures are incorporated in the housing. In other words, ifa temperature control requirement for an individual component changes,and thus an associated heat sink structure needs to be re-designed, thisre-design does not require a re-design of the casing 10.

The casing 10 further comprises mounting brackets 50, 52 for mountingthe casing 10 onto a rack structure (not shown).

FIG. 3 shows the casing 10 including the top cover 12 and with thecomponents of a WDM add/drop unit inserted, e.g. components 30, 36, and34.

In an optional modification of the casing 10, shown in FIG. 4, fans 41,43 are mounted onto the backplane 32 in the space between the sets offins 44, 46, and 48. The fans 41, 43 are disposed in a manner such thatthey generate an airflow substantially in the plane of the casing 10 andparallel to the fins. The embodiment shown in FIG. 4 is suitable forsituations where limited space is provided around the set of fins 44,46, and 48 when the casing 10 is mounted onto a rack (not shown), tofacilitate maintaining a controlled temperature environment of the WDMadd/drop multiplexer unit. It will be appreciated by the person skilledin the art that, depending on requirements, only one or more than twofans may be provided in alternative embodiments.

In another embodiment shown in FIG. 5, a casing 300 again comprises twoheat sink openings 338, 342 for receiving heat sink structures 344, 348of components 330, 334 of a WDM add/drop multiplexer unit. However, inthis embodiment the casing 300 comprises a heat sink unit in the form ofa set of fins 346 and heat pipes e.g. 347 externally mounted on abackplane 332 of the casing 300. Additional components, e.g. 336 of theWDM add/drop multiplexer unit, which are inserted into the casing 300,do not contain integral heat sink structures, but rather they areadapted to thermally connect to the set of fins 346 and the heat pipese.g. 347, when inserted. The thermal connection is adapted to bereleasable for replacement of such components, e.g. 336. Suitableimplementations for achieving such releasable thermal connection includebiasing mechanisms such as straps, levers, cams, or springs.

In the example embodiment shown in FIG. 5, the material of the backplane332 of the casing 300 and the material in an abutment portion ofadditional components e.g. 336, have thermal expansion coefficientsworking in conjunction to determine the tolerances of the modules. Inthe example embodiment, a thermal mismatch was chosen such that thermalcommunication at the interface is of lower quality at low temperatures,and of better quality in normal or hotter temperature conditions. Thisallows local heat generated by components (not shown) to be used tomaintain a high enough operating temperature at low ambienttemperatures, which in turn can reduce the size of or make unnecessaryadditional heat sources for use at such low ambient temperatureconditions.

The “hybrid” solution of combining heat sink openings e.g. 338 with aheat sink structure mounted onto the actual casing 300 can provide analternative of design for best overall thermal performance of the WDMadd/drop multiplexer unit. Parameters to be considered in choosing theoptimum design are expected to include the relationship between thespace consumed by an individual component and the heat it generates, andthe size-requirements of the backplane to provide the electricalinterconnections between the components.

In yet another embodiment shown in FIG. 6, a casing 450 again comprisestwo heat sink openings 488, 492 for receiving heat sink structures ofcomponents of a WDM add/drop multiplexer unit (not shown). In thisembodiment, the backplane 482 of the casing 450 comprises a number ofelectrical connectors, e.g. 452, 454 and a series of four connectors456.

In FIG. 7, a component for insertion into the casing 450 (FIG. 6) forelectrical contact with one of the electrical connects 456 (FIG. 6) inthe form of a tributary interface module 500 is shown. Arrow 501indicates the insertion direction for clarity. The module 500 has acorresponding electrical connector 502 for making electrical contactwith one of the connectors 456 (FIG. 6) when fully inserted into thecasing 450 (FIG. 6). When inserted, the module 500 makes thermal contactwith the heat sink surface 449 (FIG. 6) via a thermally conductivemalleable pad portion 504 of a chassis member 506 of the module 500. Itwill be appreciated by the person skilled in the art that through use ofthe thermal pad portion 504, a desired thermal conductivity between themodule 500 and the heat sink surface 449 (FIG. 6) can be maintained overa large temperature range, despite potential mismatch in thermalexpansion coefficients of the material of the chassis 506 when comparedwith the material of the heat sink surface 449 (FIG. 6). It will also beappreciated by the person skilled in the art that the malleable padportion 504 can also accommodate mechanical hardware mismatch as aresult of hardware manufacturing variation of the various hardwareelements. The term “malleable” is intended to refer to the ability ofthe pad portion 504 to be capable of being deformed, preferablyelastically, in order to establish thermal contact between the chassismember 506 and the heat sink surface 449 over a range of distancesbetween the heat sink surface 449 and the chassis member 506 (in theregion of the malleable pad portion 504 when the module 500 is fullyinserted.

The module 500 further comprises a biasing mechanism 510 consisting of aspring loaded mounting member 512 (spring 514). The mounting member 512comprises two teeth elements 516, 518 which engage into correspondingreceiving slots on a cover (not shown) of the casing 450 (FIG. 6) whenthe module 500 is fully inserted. It will be appreciated by the personskilled in the art that accordingly the thermal (and electrical)connection between the module 500 and the heat sink surface 449 (FIG. 6)is biased to accommodate relative dimensional changes caused e.g. bydifferent thermal expansion of the various materials.

It will be appreciated by the person skilled in the art that other knownbiasing mechanisms may be used in different embodiments to maintain thedesired thermal contact between the module 500 and the heat sink surface(FIG. 6), such as straps, levers, or cams.

FIG. 8 shows a front view of the module 500, showing more clearlydetails of the biasing mechanism 510. Arrow 503 indicates the insertiondirection for clarity.

As illustrated in FIGS. 7 and 8, a heat pipe 508 is further embedded inthe chassis member 506 of the module 500 utilising suitable groovesformed in the chassis 506. During operation, heat transfer from heatgenerating components within the module 500 (not shown), which aremounted onto the inside of the chassis 506 and cover members e.g. 507,is facilitated through the embedded heat pipe 508 and towards the heatsink surface (FIG. 6) when the module 500 is inserted into the casing450 (FIG. 6). In the example embodiment, the heat pipe 508 comprises acopper heat pipe filled with water as a working fluid. In the exampleembodiment, water as the working fluid is suitable because it has aconvenient freezing temperature of 0° C., which closes off the operationof the heat pipe 508 in cold conditions, i.e. when heat generated bycomponents within the module 500 is advantageous to maintain a suitableoperating temperature within the module 500. However, it will beappreciated by the person skilled in the art that other heat pipedesigns can be selected in different embodiments, such as heat pipesmade from different material and/or containing a different workingfluid, or highly thermally conductive members in the form of diamond orgraphite strips or rods.

It is noted that in the embodiments described above with reference toFIGS. 1 to 8, the design of the respective set of fins 44, 46, 48 and344, 346, 348 is chosen such that the casings may be mountedhorizontally or vertically. The fins are substantially planar anddisposed parallel to the backwall of the casing. Furthermore, the heatpipes are formed longitudinally and without bends. It will beappreciated by the person skilled in the art, that accordingly, airflowbetween the fins is enabled with reduced, and preferably minimumrestriction in either a horizontal or vertical mounting position.

Furthermore, the embodiments described above with reference to FIGS. 1to 8 are dimensioned to fit into a 19 inch rack, and have a height ofone rack unit. Alternatively the unit can be dimensioned to fit in a 23inch rack. However, it will be appreciated by the person skilled in theart that the present invention is not limited to a particular overallsize.

In yet another embodiment schematically shown in FIG. 9, for a casing400 which is to be vertically mounted, the casing 400 may comprisebaffle structures 402, 404 disposed between sets of fins 406, 408 and410. In this embodiment, the set of fins 406, 410 are formed integrallywith components (not shown) inserted into the casing 400 and extendingthrough heat sink openings 411, 412 of the casing 400. The fins 408 aremounted on a backplane 413 of the casing 400, and interconnect(releasably) to other components (not shown) inserted into the casing400.

The baffle structures 402, 404 are disposed in a manner such thatconvection airflow from one set of fins is diverted from the other setsof fins as indicated by arrows 414. It will be appreciated by the personskilled in the art, that thus a successive heating of the convection airfrom the lowest set of fins 406 to the highest set of fins 410 can bereduced, and preferably be avoided.

Turning now to FIG. 10, there is shown a chassis member 60 for carryinga plurality of circuit boards (not shown). The chassis member 60 isformed from a material having thermal characteristics suitable such thatthe chassis member 60 can, in use, function as a heat sink for heatgenerating electrical components (not shown) on the circuit boards (notshown) carried on the chassis member 60. In the example embodiment, thechassis member is formed form a zinc aluminium alloy.

Furthermore, the main body 62 of the chassis member 60 is contoured orshaped in a manner such that a distance between individual heatgenerating components (not shown) on the circuit boards (not shown) andregions of the main body facing the heat generating components isreduced compared to other components (not shown) on the circuit boards(not shown).

For example, the main body 62 comprises a raised portion 64 disposed ina manner such that, when a circuit board containing a particular heatgenerating electrical component is mounted on the chassis member 60, adistance between the top surface 66 of the raised portion 64 and theheat generating component (not shown) is reduced compared to othercomponents (not shown) on the board (not shown).

The chassis member further comprises side wall structures 66, 68, 70 and72 substantially around the peripheral region of the main body 62. Theside wall portions 66, 68, 70 and 72 are formed integrally with and fromthe same material as the main body 62, and are adapted to function as atleast portions of housing side walls of a housing structure (not shown)for the circuit boards (not shown) carried by the chassis member 60 andforming a WDM multiplexer module.

The chassis member 60 is further designed in a manner such thatadditional circuit boards (not shown) can be mounted to the “underside”74 of the main body 62.

Turning now to FIG. 11, there are shown parts of a WDM multiplexermodule 80 comprising a chassis member 82 and a heat sink structure 84.The heat sink structure 84 comprises a plurality of fins e.g. 86 mountedon to three water based heat pipes 88, 90 and 92, extending throughslots 94, 96, 98 respectively of a side wall portion 100 of the chassismember 82. The heat sink structure 84 further comprises four protectivemounting rods e.g. 102 disposed in a manner such as to relief the heatpipes 88, 90, 92 from excessive load bearing as a result of a forcebeing applied to one or more of the fins 86.

The heat pipes 88, 90, and 92 are mounted inside the WDM multiplexermodule 80 and onto a main body 104 of the chassis member 82 by way of athermally conducting mounting bracket 106. A TE device in the form of athermoelectric conductor/cooler (TEC) 108 is located underneath themounting bracket 106 and thermally connected to the main body 104 of thechassis member 82.

A local thermal environment structure including, in the exampleembodiment a laser housing 110 is mounted inside of the WDM multiplexermodule 80 by way of a vertically mounted circuit board 112. Foursemiconductor laser elements 114, 116, 118, and 120 are mounted in amanner such that their respective junction regions are locatedsubstantially inside or immediately adjacent to a thermally conductivebase member 122 inserted in the laser housing 110, forming, in theexample embodiment, the local thermal environment structure. A secondTEC 124 is mounted on the main body 104 of the chassis member 82 and inthermal contact with base member 122 and thus with the laser structure110.

It is noted that in the example embodiment illustrated in FIG. 11, thelaser drivers (not shown) associated with the lasers 114, 116, 118 and120 will be located outside the laser housing 110, i.e. outside thelocal thermal environment created within the laser housing 110 (andconductive base member 122). The laser drivers (not shown) in theassembled module will be located on a circuit board (not shown) mountedon the main body 104 of the chassis member 82, i.e. their thermalenvironment will be governed by the “primary” thermal environment insidethe module 80. It has been found that laser drivers rated to atemperature range that is compatible with the primary thermalenvironment are available for the design of the example embodiment.

Furthermore, it is noted that the TEC 124 electrically isolates thelaser 114, 116, 118, and 120 from the chassis member 82. This has beenfound to improve the operation of the lasers, e.g. in terms ofachievable bit rate.

In the following, operation of the heat control features of the WDMmultiplexer module 80 to create a controlled temperature environmentinside thereof will be described for an example setting of first andsecond stage temperature ranges.

For the purpose of this description, a maximum temperature range for anOSP situation is assumed to be from −40° C. to +65° C.

In the high temperature extreme ambient situation of +65° C., thetemperature inside the WDM multiplexer module 80 may be estimated toreach 85° C., due to heat generation from electronic devices (not shown)incorporated in the WDM multiplexer module 80. This is with only theheat sink structure comprising heat pipes 88, 90, 92 and the set of fins84 considered at this stage.

In the example embodiment, the first stage temperature control iscompleted through utilising the first TEC 108 to reduce the temperatureinside the WDM multiplexer module 80° C. With the TEC 108 beingthermally connected to the thermally conducting chassis member 82, itwill be appreciated that a relatively homogenous temperature profile canbe achieved inside the WDM multiplexer module 80.

For the majority of components incorporated in the WDM multiplexermodule 80, this maximum temperature of 80° C. is tolerable. However, inthe example embodiment shown in FIG. 5, the lasers 114, 116, 118 and 120are to be kept in a more tightly confined temperature range for specificreasons, including laser emission efficiency, wavelength stability, andaccommodation of component variances between different lasers.

Accordingly, in a second stage temperature control, the 80° C.environment inside the WDM multiplexer module 80 is locally reducedaround the respective junctions of the lasers 114, 116, 118 and 120 byway of TEC 124 and via and the thermally conductive base element 122located inside the laser housing 110. In the example embodiment, thetemperature around the respective junctions of the lasers 114, 116, 118,and 120 is reduced from +80° C. inside the WDM multiplexer module 80 to+50° C. in and around the base element 122 for the high temperatureextreme ambient situation.

At the low temperature extreme ambient situation of −40° C., it isassumed that the operation of heat generating components (not shown)inside the WDM multiplexer module 80 will again increase the temperatureinside the WDM multiplexer module 80 by 20° C. to −20° C. However, it isnoted that due to variations in heating efficiencies with temperatureand/or due to the fact that the water based heat pipes 88, 90, 92, whichfreeze below substantially 0° C., create a discontinuity in heattransfer to the set of fins 84, the temperature increase inside the WDMmultiplexer module 80 as a result of heat generation from the heatgenerating components may be larger than 20° C. However, if forillustrative purposes a temperature increase to −20° C. is assumed, thefirst stage temperature control in addition comprises utilising the TEC108 to increase the temperature inside the WDM multiplexer module 80 bya further 20° C. to 0° C.

Accordingly, the first stage temperature control has “buffered” theambient temperature range of −40° to +65° to a temperature range of 0°C. to +80° C. inside the WDM multiplexer module 80. It is noted thatwhile the high temperature end point is increased due to the internalheat generation, the overall range is reduced. It has been found thatthe WDM multiplexer module 80 can be designed in a manner such that thistemperature range is tolerable for most of its components in an OSPsituation.

Again, the lasers 114, 116, 118 and 120 do, however, require a moretightly confined temperature range, and thus the local thermalenvironment around the respective junctions of the lasers 114, 116, 118and 120 at the low temperature end is “lifted” by a farther 40° C. to+40° C. utilising TEC 124.

As a result, the second stage temperature environment range is from +40°C. to +50° C., for an ambient temperature range of −40° C. to +65° C. Ithas been found that this temperature range is satisfactory forconstruction of a WDM multiplexer module for use in an OSP situation.

FIG. 12 shows an assembled WDM multiplexer module 130 embodying thepresent invention and suitable for use in an OSP situation. A housingstructure comprising covers 132 and 134 is completed by side wallportions e.g. 136 of a chassis' member 138 of the WDM multiplexer module130. On the front plane 140 of the WDM multiplexer module 130, suitableconnections/connectors are provided, including to a trunk optical fibrenetwork link 142 and a power connection 144. The housing structure isfurther designed in a manner such that it functions as an EMI shield forthe internal components of the WDM multiplexer module 130.

FIG. 13 shows another chassis member 550 for a WDM multiplexer module,embodying the present invention and suitable for use in an OSPsituation. The chassis member 550 comprises embedded heat pipes 552,554, 556 and 557 a, b. Similar to the functioning of heat pipe 508described above with reference to FIGS. 7 and 8, in use the heat pipes552, 554 and 556 facilitate transfer of heat from heat generatingcomponents (not shown) towards a heat sink structure in the form of aset of heat fins 558 mounted directly to the heat pipes 552, 554 and 556extending out from the main body of the chassis member 550. In theexample embodiment, the chassis member 550 is made from an aluminiumalloy, because it is machinable and light weight, thus facilitating massmanufacture and physical implementation requirements. In the exampleembodiment, to improve the thermal conductive properties of the chassis550, the embedded heat pipes 552, 554, and 556 are utilised. Again, thesurface e.g. upper surface 562 of the chassis member 550 is contoured tomeet desired heat transfer requirements between the chassis member 550and individual heat generating components (not shown) on a circuit board(not shown) mounted onto the chassis member 550.

In the example embodiment the heat pipes 552, 554, 556 and 557 a, b arein the form of copper heat pipes filled with water as a working fluid,thus again utilising the convenient freezing temperature of 0° C. to cutoff heat transfer through the pipes 552, 554, 556 at low temperatures.However, it will be appreciated by the person skilled in the art thatdifferent heat pipe designs can be chosen in different embodiments ofthe present invention to meet desired requirements.

It will further be appreciated by the person skilled in the art, thatthe inventive concept of “embedded” heat pipes to improve heat transferin a chassis member can be implemented in different ways withoutdeparting from the spirit or scope of that inventive concept. Forexample, in alternative embodiment heat pipes of any shape could beglued or otherwise mounted to a surface of a chassis member, i.e.without provision of grooves. In yet another embodiment, holes could bedrilled through the chassis member to accommodate heat pipes. In yetanother embodiment, the chassis member could be formed from more thanone part with channels formed in at least one part so that when theseparate parts are brought together to form the chassis, conduits areformed which can contain a suitable working fluid.

In the following, some further features of a WDM multiplexer moduleembodying the present invention will be described for start-up orre-start scenarios at the low temperature end of an OSP situation. Atthe low temperature end of −40° C., it may be detrimental to power upall of the electrical components of the WDM multiplexer structure atonce. It is assumed that in the start-up or re-start situation, allpower was initially cut, i.e. the TECs are also inoperable.

Some of the components may either malfunction or even break down whenoperated at such low temperatures. Accordingly, in an embodiment of thepresent invention, a control unit is utilised to sequentially power upgroups and/or individual ones of the internal electrical components,based on operating temperature specifications and heat generatingcharacteristics of the electrical components. This (a) saves thosecomponents not suitable for power up from malfunction/breakdown, and (b)forms the first step of a first stage temperature control similar to theone described above with reference to FIG. 5, i.e. it facilitates atemperature increase inside the WDM multiplexer module due to heatgeneration from the powered up components. When or as the temperature israised internally due to the heat generation, remaining components arepowered up in a then increased temperature environment designed to besafe for those components.

In the following, the functionality of a WDM add/drop multiplexerstructure for use at a node in an optical Access network embodying thepresent invention will be described with reference to FIGS. 14 and 15.

FIG. 14 shows a schematic diagram of a network node structure 200 foruse in an Access WDM network embodying the present invention. The nodestructure 200 comprises two network interface modules 212, 214, anelectrical connection motherboard 216 and a plurality of tributaryinterface modules e.g. 218. The network interface modules 212, 214, theelectrical connection motherboard 216 and the plurality of tributaryinterface modules e.g. 218 compare with items 30, 34, 32, and 36respectively in FIG. 2.

Returning to FIG. 14, the network interface modules 212, 214 areconnected to an optical network east trunk 220 and an optical networkwest trunk 222 respectively, of a WDM optical network (not shown) towhich the network node structure 210 is connected in-line. The WDMoptical network may for example be arranged as a WDM optical ringnetwork, or as a WDM linear optical network.

Each of the network interface modules 212, 214 comprises the followingcomponents:

a passive CWDM component 224, in the exemplary embodiment a 8 wavelengthcomponent;

an electrical switch component, in the exemplary embodiment a 16×16switch 226;

a microprocessor 228;

a plurality of receiver trunk interface cards e.g. 230; and

a plurality of transmitter trunk interface cards e.g. 232, and

a plurality of electrical regeneration unit e.g. 240 associated witheach receiver trunk interface card e.g. 230.

Each regeneration unit e.g. 240 performs 3R regeneration on theelectrical channels signal converted from a corresponding optical WDMchannel signal received at the respective receiver trunk interface carde.g. 230. Accordingly, the network node structure 200 can provide signalregeneration capability for each channel signal combined with anelectrical switching capability for add/drop functionality, i.e.avoiding high optical losses incurred in optical add/drop multiplexers(OADMs).

Details of the receiver trunk interface cards e.g. 230 and regenerationunit e.g. 240 of the exemplary embodiment will now be described withreference to FIG. 15.

In FIG. 15, the regeneration component 240 comprises a linear opticalreceiver 241 of the receiver trunk interface card 230. The linearoptical receiver 241 comprises a transimpendence amplifier (not shown)i.e. 1R regeneration is performed on the electrical receiver signalwithin the linear optical receiver 241.

The regeneration unit 240 further comprises an AC coupler 256 and abinary detector component 258 formed on the receiver trunk interfacecard 230. Together the AC coupler 256 and the binary detector 258 form a2R regeneration section 260 of the regeneration unit 240.

The regeneration unit 240 further comprises a programmable phase lockloop (PLL) 250 tapped to an electrical input line 252 and connected to aflip flop 254. The programmable PLL 250 and the flip flop 254 form aprogrammable clock data recovery (CDR) section 255 of the regenerationunit 240.

It will be appreciated by a person skilled in the art that at the output262 of the programmable CDR section 255 the electrical receiver signal(converted from the received optical CWDM channel signal over opticalfibre input 264) is thus 3R regenerated. It is noted that in the exampleshown in FIG. 15, a 2R bypass connection 266 is provided, to bypass theprogrammable CDR section 255 if desired.

Returning now to FIG. 14, each of the tributary interface modules e.g.218 comprises a tributary transceiver interface card 234 and anelectrical performance monitoring unit 236. A 3R regeneration unit (notshown) similar to the one described in relation to the receiver trunkinterface cards e.g. 230 with reference to FIG. 11 is provided.Accordingly, 3R regeneration is conducted on each received electricalsignal converted from received optical input signals prior to the 16×16switch 226.

As can be seen from the connectivity provided through the electricalmotherboard 216, each of the electrical switches 226 facilitates thatany trunk interface card e.g. 230, 232 or tributary interface card e.g.218 can be connected to any one or more trunk interface card e.g. 230,232, or tributary interface card e.g. 218. Accordingly, e.g. eachwavelength channel signal received at the western network interfacemodule 214, e.g. at receiver trunk interface card 238 can be dropped atthe network node associated with the network node structure 200 via anyone of the tributary interface modules e.g. 218, and/or can be throughconnected into the optical network trunk east 220 via the east networkinterface module 212.

Furthermore, it will also be appreciated by the person skilled in theart that the network node structure 200 is west-east/east-west traffictransparent. Also, due to the utilisation of network interface modules212, 214 which each incorporate a 16×16 switch 226, a redundant switchis readily provided for the purpose of protecting the tributaryinterface cards e.g. 218 from a single point of failure. The tributaryinterface cards e.g. 218 are capable of selecting to transmit a signalto either (or both) network interface modules 212, 214 and theassociated switches e.g 226. The function of the switches e.g. 226 is toselect the wavelength and direction that the optical signal receivedfrom the tributary interface cards e.g. 218 will be transmitted on andinto the optical network.

One of the advantages of the network structure 200 (FIG. 14) is that theelectronic switches support broadcast and multicast transmissions of thesame signal over multiple wavelengths. This can have useful applicationsin entertainment video or data casting implementation. Many opticaladd/drop solutions do not support this feature, instead, they onlysupport logical point-point connections since the signal is dropped atthe destination node and does not continue to the next node.

It will be appreciated by the person skilled in the art that numerousmodifications and/or variations may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

In the claims that follow and in the summary of the invention, exceptwhere the context requires otherwise due to express language ornecessary implication the word “comprising” is used in the sense of“including”, i.e. the features specified may be associated with furtherfeatures in various embodiments of the invention.

What is claimed is:
 1. A casing member for a WDM add/drop multiplexerunit, the casing member comprising: a backplane for interconnection ofcomponents of the WDM add/drop multiplexer unit inserted in the casingmember, and at least one heat sink opening formed in a wall of thecasing member disposed for receiving a heat sink structure of acomponent of the WDM add/drop multiplexer unit in a manner such that theheat sink structure is exposed to an ambient around the casing memberwhen the component is mounted in the casing member, for facilitatingmaintaining a controlled temperature environment inside of thecomponent.
 2. The casing member as claimed in claim 1, wherein the heatsink opening is formed in a backwall incorporating the backplane.
 3. Thecasing member as claimed in claim 2, wherein a pair of heat sinkopenings is formed in a mirrored configuration on either side of thebackplane with respect to a centreplane halfway along the width of thecasing member.
 4. The casing member as claimed in claim 3, wherein thecasing member further comprises a first key member arranged forpreventing a component of the WDM add/drop multiplexer unit fromcontacting the backplane, when said component is inserted with anincorrect orientation, and wherein the first key member is adapted forcooperation with a heat sink structure of said component.
 5. The casingmember as claimed in claim 3 or 4, wherein the casing member furthercomprises a second key member arranged for preventing a component of theWDN add/drop multiplexer unit from contacting the backplane, when saidcomponent is inserted with a correct orientation in a slot intended foranother component, and wherein the second key member is adapted forcooperation with a third key member formed on said component.
 6. Thecasing member as claimed in claim 1 or 2, wherein the casing memberfurther comprises at least one vent opening in one wall of the casingmember.
 7. The casing member as claimed in claim 6, wherein the casingmember comprises at least one pair of vent openings, the openings of thepair being formed in opposite walls of the casing member.
 8. The casingmember as claimed in claim 7, wherein the at least one pair of ventopenings is formed in the sidewalls of the casing member.
 9. The casingmember as claimed in claim 7, wherein at least one pair of vent openingsis formed in the top and bottom walls of the casing member.
 10. Thecasing member as claimed in claim 1, wherein the casing member isadapted for mounting horizontally or vertically.
 11. The casing memberas claimed in claim 1, wherein the casing member further comprises aheat sink unit mounted onto the casing member and adapted, whencomponents of the WDM add/drop multiplexer unit are inserted in thecasing member, for making thermal contact with at least one of thecomponents, for facilitating maintaining a controlled temperatureenvironment inside of said at least one of the components.
 12. Thecasing member as claimed in claim 11, wherein the casing membercomprises a locking member arranged for cooperation with a correspondinglocking member of one of the components when said one of the componentsis inserted to maintain the thermal contact.
 13. The casing member asclaimed in claim 12, wherein the locking member is arranged forcooperation with the corresponding locking member to bias the said oneof the components when inserted.
 14. The casing member as claimed inclaim 11, wherein the heat sink unit is arranged for a releasableinterconnection to said component.
 15. The casing member as claimed inclaim 11, wherein the heat sink unit is incorporated in a backwallincorporating the backplane.
 16. The casing member as claimed in claim15, wherein the heat sink unit is formed on the backplane.
 17. Thecasing member as claimed in claim 11, wherein the heat sink unitcomprises a plurality of substantially planar fins disposedsubstantially parallel to a backwall of the casing member, and mountedby way of at least one longitudinal mounting member expandingsubstantially perpendicularly from the backwall.
 18. The casing memberas claimed in claim 1, wherein the casing member further comprises atleast one fan device mounted on the outside of the casing member anddisposed, when the heat sink structure of the component of the WDMadd/drop multiplexer unit extends through the heat sink opening of thecasing member, for subjecting the heat sink structure to an airflowgenerated by the at least one fan device.
 19. The casing member asclaimed in claim 1, wherein the casing member further comprises at leastone baffle structure externally mounted or formed on the casing memberfor diverting, when the casing member is mounted vertically, convectionairflow from one heat sink structure or heat sink unit away from otherheat sink structures or heat sink units.